The present invention relates to an apparatus for continuously measuring the elemental content of a slurry independently of the slurry density and slurry composition by utilizing X-ray fluorescence analysis.
Due to the rising worldwide need for raw materials, it is increasingly necessary to mine deposits having a low content of the desired raw material. Such deposits are primarily exploited with the use of the flotation method. In the flotation method, valuable mineral is obtained from an aerated suspension of finely ground raw materials and water, a so-called flotation slurry, with the aid of chemicals. Use of this method requires continuous analysis of the product streams to insure economic operation of facilities which often include widely branched-out slurry conduits. Analytical devices are required which quickly indicate the mineral contents of interest at strategically important points in the process to make it possible to quickly intervene in the operation of the process. This is particularly necessary when monitoring the waste streams and the concentrate streams leaving the production facility. Losses of valuable minerals in the waste stream result in considerable financial erosion in the operation of such a facility.
Further, the quality requirements imposed by the processing industry which uses the resultant concentrates are very high and can be met only with difficulty. The industry requirements not only relate to providing concentrates with a specific content of valuable mineral, but also to providing the concentrates with precise proportions of so-called deleterious components. Exceeding such proportions can lead to considerable financial losses and can result in having to discard the entire product.
It is customary to conduct the control of the process streams by means of wet chemical analysis, especially in relatively small flotation plants. This analysis method cannot be effected continuously and requires a considerable amount of time. Using wet analysis it is initially necessary to withdraw samples from the product streams and to process these samples appropriately by drying, grinding, homogenizing, etc., before analysis can begin. Using such wet chemical analysis methods, a time delay of several hours up to a day can be expected from the time the sample is taken to the time the result of analysis is obtained. As a result, entire daily productions, on occasion, may have to be discarded.
Time-consuming wet chemical analysis is being replaced in part by X-ray fluorescence. In this method, dispersive, conventional, multichannel X-ray spectrometers excited by an X-ray tube are used. Although a substantial saving in time is obtained as compared with wet chemical analysis, use of these devices still involves an undesirable time delay between the taking of the sample and the analytical result caused by the necessary preparation of the sample.
Only a continuous, rapid, and highly responsive quality control promotes efficient production by a controlled intervention in the process operation. In order to reduce the time delay occurring between the taking of the sample and the analytical result, devices and processes have been developed which make it possible to carry out a direct analysis at the product stream. In this context, mention is made of the on-stream analysis system Courier 300 developed by the company Outokumpu Oy of Finland. This device is, in principle, a continuously operating sample-taking system with discontinuous analysis based on X-ray fluoresence. In this process, a partial product stream is drawn via pumps and pipelines from various sample taking points in the flotation plant and conducted to a battery of measuring cells. A movable measuring head with X-ray tube and analytical section travels at predetermined time intervals along the various cells and determines in a quasi-continuous fashion the elemental contents of the individual slurry streams. This arrangement, however, is very expensive and it is difficult to financially justify it for use in relatively small flotation plants.
So-called immersion probes have also been developed. In contrast to the conventional X-ray fluorescence method, these devices utilize excitation by an isotope source in place of excitation by an X-ray tube. The immersion probes are hung in the slurry stream. In the case of flotation plants, for example, they are hung in the so-called flotation cells. One disadvantage in this method is the inhomogeneity of the slurry usual in flotation cells. Further, an additional density measuring probe is necessary in all cases. Such immersion probes have been developed by the companies Outokumpu Oy of Finland, Philips of Australia, and NUTMAQ of England.
All of the on-line analysis devices heretofore developed on the basis of X-ray fluorescence initially determine the element content of the slurry. The determination of the element content in the solid matter, however, requires an additional measurement of the slurry density. Because densimeters operate accurately only in a bicomponent system of liquid/solid matter, the measurements can be in error due, for example, to air occlusions which often occur in the slurry in flotation processes. This is a disadvantage of conventional X-ray fluorescence analysis (XRFA) processes.
In addition to the devices operating on the basis of X-ray fluorescence, there are also on-line analysis devices operating according to the principle of neutron activation analysis. In these devices, a partial slurry stream first flows continuously through an irradiation cell with the neutron source. The slurry is "activated" at this point and then flows via an inductive flowmeter into a measuring cell provided with a detector where the induced activity is measured. During blackflow, the slurry passes a densimeter. The required use of the densimeter in the neutron activation analysis process results in the same disadvantages noted above in the X-ray fluorescence analysis process. Furthermore, in the neutron activation analysis process a specific slurry throughflow must be maintained constant at all times.
In our prior filed U.S. patent application, Ser. No. 141,698 now U.S. Pat. No. 4,388,530 we disclose an apparatus utilizing X-ray fluorescence to provide for the rapid and continuous element analysis of a process stream. In that apparatus a measuring chamber with a slurry flow channel is provided at each side with a measuring window. The detector is disposed behind one measuring window and a primary radiation source and a target are disposed behind the other measuring window. The transmitted pimary and target radiation as well as excited X-ray radiation are detected by the detector. This design of the measuring chamber, however, is not sufficient when determining, for example, the content of Pb in the slurry due to the low X-ray yield of Pb in that chamber geometry.